08:12:34 a.m. - Acquisition of signal by NASA's TDRS-West communications satellite.

08:10:39 a.m. - APU-2 startup.

08:15:30 a.m. - Deorbit ignition. Change in velocity: 176 mph; Burn duration: two minutes and 38 seconds. Location (latitude/longitude in minutes:seconds): 33:35 S/98:10 E; altitude: 175.95 statute miles. Velocity: 17,319.7 mph

08:18:08 a.m. - Deorbit burn complete.

08:26:09 a.m. - Forward reaction control system propellant dump begins.

08:27:12 a.m. - FRCS dump complete.

08:31:25 a.m. - APU-1 startup. Entry interface minus 13 minutes.

08:31:29 a.m. - APU-3 startup.

08:31:57 a.m. - APU-1 at normal operating pressure.

08:31:59 a.m. - APU-2 at normal operating pressure.

08:32:01 a.m. - APU-3 at normal operating pressure.

08:32:29 a.m. - Shuttle main engine stow sequence begins (thrust vector control system isolation valve 1 to close).

08:34:09 a.m. - OEX recorder activation; entry interface - EI - minus 10 minutes.

08:39:09 a.m. - EI-5 minutes (OPS-304 PRO). Mach: 24.40.

08:39:11 a.m. - Speedbrake close; rudder commanded to zero degrees.

Editor's note: For clarity, mission control audio and cockpit voice loops have been omitted to this point. All conversations were normal and thus have no significance to the accident investigation. We pick up the timeline roughly two minutes before entry interface, the point where the shuttle enters the discernible atmosphere 400,000 feet above the Pacific Ocean.

08:41:35 a.m. - STS-ICOM: Commander Rick Husband: "Two minutes to entry interface."

08:41:43 a.m. - STS-ICOM: Laurel Clark: "I know about the line cable, Willie, I didn't understand your question. You don't want the camera back, right?"

08:41:51 a.m. - STS-ICOM: Pilot William "Willie" McCool: "I do not want the camera back.

STS-ICOM: Husband: "He's got one mounted in his HUD already."

STS-ICOM: Clark: OK. Yep, yep, yep. Yep, Replug."

08:41:54 a.m. - MCC-Commentator: "This is mission control, Houston. Columbia's altitude is now 90 miles above the Pacific Ocean to the north of the Hawaiian islands, about two minutes away from entering the Earth's atmosphere. All activities continuing to go smoothly en route toward a touchdown at the Kennedy Space Center at 8:16 a.m. Central time."

08:41:58 a.m. - STS-ICOM: McCool: "Replug, that's all you've gotta do."

08:42:08 a.m. - STS-ICOM: McCool: "When do we start moving our head around, Rick? When we start getting a little bit of Gs?"

STS-ICOM: Husband: "A little bit of Gs, yeah."

08:42:29 a.m. - STS-ICOM: Clark (operating a video camera): "KC, can you look at the camera a second? Look at me."

08:42:35 a.m. - STS-ICOM: Flight engineer Kalpana Chawla: "Me?"

STS-ICOM: Clark: Yep. Yeah. What KC?"

08:42:37 a.m. - MCC-Commentator: "Columbia is currently targeted toward runway three-three at the Kennedy Space Center, the runway selection continues to be discussed here in mission control, however. But for its approach to runway three-three, Columbia will perform a right overhead turn to align with the runway of about 214 degrees around the heading alignment cylinder, an imaginary cylinder created by the microwave landing system for the shuttle that assists in guiding it for its final approach."

08:42:38 a.m. - STS-ICOM: Chawla: "Oh, I just turn towards you, I see what you have there."

STS-ICOM: Clark: "Yeah." (laughter)

STS-ICOM: Chawla: "OK, Laurel."

08:42:51 a.m. - STS-ICOM: McCool: "Trash bag, KC, if you've got any."

STS-ICOM: Chawla: "We are gray taping, you can just give it to us."

08:42:57 a.m. - STS-ICOM: McCool: "That's six and a half bags."

STS-ICOM: Chawla: "OK, I'm going to have to give this to Laurel when she is done."

08:43:05 a.m. - STS-ICOM: Chawla: "I'm going to gray tape it behind, I mean (garble) tape it behind the seat, I think this is light enough that it will stay."

08:43:18 a.m. - STS-ICOM: McCool: "Laurel, you see lots of jets firing."

STS-ICOM: Clark: "I'm getting the jets firing, I'm trying to see if I can get an overhead window view yet."

08:43:25 a.m. - STS-ICOM: Husband: "OK. That's all I can do is three and a half bags out of four. So that'll work. If I can pass that back to you?"

08:43:32 a.m. - STS-ICOM: Chawla: "Rick, if you could wait just one second, I want to get to my gloves before Gs build, I don't want to get..."

STS-ICOM: Husband: "Certainly."

STS-ICOM: Chawla: "...two up."

STS-ICOM: Husband: "Certainly."

08:43:40 a.m. - STS-ICOM: Chawla: "Here comes (garble)."

08:43:42 a.m. - STS-ICOM: Husband: "OK. We're just past EI."

STS-ICOM: Clark: "Ok."

STS-ICOM: Chawla: "I have both gloves."

08:43:47 a.m. - STS-ICOM: Clark: "Is that jets firing on the DAP, I guess."

STS-ICOM: Chawla: "And Rick, I'll take your bag. And float it aft gently, I've got it."

08:43:58 a.m. - STS-ICOM: McCool: "That might be some plasma now."

STS-ICOM: Clark: "Think so, already?"

STS-ICOM: McCool: "Yeah, the jets are not firing right now."

STS-ICOM: Clark: "All right, it was quite a (GARBLE), actually."

STS-ICOM: McCool: "We see it out the front, also."

STS-ICOM: Husband: "That's some plasma."

08:44:09 a.m. - Actual moment of entry interface. The shuttle falls into the discernible atmosphere 395,010 feet over the Pacific Ocean at a velocity of Mach 24.57 (+30.833-167.556)

08:44:09 a.m. - STS-ICOM: Clark: "Copy, and there's some good stuff outside. I'm filming overhead right now."

STS-ICOM: McCool: "It's kind of dull."

STS-ICOM: Husband: "Oh, it'll be obvious when the time comes."

08:44:18 a.m. - STS-ICOM: Clark: "Well, Willy, I guess I could give you the camera to put out the front window."

STS-ICOM: Husband: "Here, let's, uh, no, let's don't do that."

STS-ICOM: Clark: "OK."

STS-ICOM: Husband: "Let's just, uh, let's go ahead and make sure you check your suit pressure integrity, too."

STS-ICOM: Clark: "All right."

08:44:51 a.m. - STS-ICOM: Husband: "And comm check on intercom. Put the, uh, visors down. CDR."

STS-ICOM: McCool: "PLT."

STS-ICOM: Clark: "PS1. (then laughing to correct herself) MS1."

STS-ICOM: Chawla: "I don't have my gloves on yet. MS2."

STS-ICOM: Husband: "All right, good enough."

08:45:09 a.m. - STS-ICOM: Clark: "And we're going to leave visors down, though."

STS-ICOM: Husband: "Oh, no. I'm just saying just check your suit's..."

STS-ICOM: Clark: "OK."

STS-ICOM: Husband: ".. pressure."

STS-ICOM: Clark: "And then I'm going to go back off. Yeah."

STS-ICOM: Husband: "Yeah."

08:45:16 a.m. - MCC-Commentator: "Columbia's altitude now 71 statute miles as it enters Earth's atmosphere above the Pacific Ocean en route to the Kennedy Space Center, its speed 17,000 miles per hour."

08:45:20 a.m. - STS-ICOM: Husband: "That's good enough for (GARBLE), I'm going to check one other thing."

08:45:32 a.m. - STS-ICOM: McCool: "Starting to glow a little bit more now, Laurel."

STS-ICOM: Husband: "Yeah... OK, all that's worked."

08:45:42 a.m. - MCC-Commentator: "Columbia with wings level and nose angled up at about 40 degrees to control heating as it descends into the atmosphere. It's altitude now 68 miles. As Columbia descends into the atmosphere and approaches the continental United States it'll perform the first in a series of four banks it performs as it approaches the Kennedy Space Center. That first bank to the right, then back to the left, then back to the right and then a final bank to the left as it approaches Kennedy and the Shuttle Landing Facility runway. Those designed to dissipate speed for the shuttle as it descends into the atmosphere toward landing."

08:45:49 a.m. - STS-ICOM: Husband: "It's noisy in there, isn't it?

08:45:52 a.m. - STS-ICOM: McCool: "Do see it over my shoulder now, Laurel?"

STS-ICOM: Clark: "I was filming, it doesn't show up nearly as much as the back."

08:45:58 a.m. - STS-ICOM: McCool: "It's going pretty good, now. Ilan, it's really neat, just a bright orange yellow out over the nose, all around the nose."

08:46:10 a.m. - STS-ICOM: Husband: "Wait until you start seeing the swirl patterns out your left and right windows."

STS-ICOM: McCool: "Wow."

STS-ICOM: Husband: "Looks like a blast furnace."

08:46:31 a.m. - STS-ICOM: Husband: "Let's see here... look at that.

STS-ICOM: McCool: "Yep, we're getting some gees.

STS-ICOM: Husband: "Yeah."

STS-ICOM: McCool: "I let go of a card, and it falls."

08:46:26 a.m. - MCC-FLIGHT: "OK, FDO, go ahead."

MCC-FDO: "This data set is a spliced data set. This is my back room's attempt to, uh, get us some data off that first balloon that was broken. And it shows us 11 hundred 60 feet at the close-in aim point."

MCC-FLIGHT: "With the close..."

MCC-FDO: "Yes sir. And we're waiting for our re-release balloon, which was just released a few minutes ago."

MCC-FLIGHT: "OK. Now, uh, we lost the balloon at 6,000 feet and, did we get it back at some point? Or when you say 'spliced it together,' I mean, I don't want, I don't know whether I should..."

08:46:30 a.m. - MCC-Commentator: "Just under 30 minutes to touchdown for Columbia now, altitude 64 miles."

08:46:39 a.m. - STS-ICOM: McCool: I got a bit flip here on the accel now."

08:46:48 a.m. - Qbar equals 0.5 pounds per square foot. Mach: 24.66

STS-ICOM: Husband: "Yep. Alright, we're at, uh, hundredth of a G."

08:46:51 a.m. - STS-ICOM: McCool: "This is amazing, it's really getting, uh, fairly bright out there."

08:46:56 a.m. - STS-ICOM: Husband: "Yep. Yeah, you definitely don't want to be outside now."

08:47:00 a.m. - MCC-FDO: "We did not, we did not get any data beneath 6K, I mean above 6K, excuse me...

08:47:01 a.m. - STS-ICOM: Chawla: "What, like we did before?

STS-ICOM: (laughter)

08:47:03 a.m. - MCC-FLIGHT: "OK."

MCC-FDO: "... and we spliced basically a previous data set..."

MCC-FLIGHT: "I got you."

MCC-FDO: "... on top of this one to give us an estimate."

08:47:03 a.m. - STS-ICOM: McCool: "How's it look out the back, Laurel?"

STS-ICOM: Husband (responding to Chawla): "Good point."

STS-ICOM: Clark: "Uh..."

08:47:09 a.m. - STS-ICOM: Clark(?): "Willie, I can see you in your mirror."

STS-ICOM: McCool: "Not yet?"

08:47:11 a.m. - MCC-FLIGHT: "Now let's see, from where we're releasing the balloons to, which way... are they going out over the water with the wind direction from the surface on up to about 10,000 feet, the direction is roughly out of the west, isn't it?"

MCC-FDO: "Yes, flight, they are going out the water, out over the water, I concur with that, we are..."

MCC-FLIGHT: "We start out with them far enough away from where our HAC really is and then they're going the wrong way."

08:47:14 a.m. - STS-ICOM: Clark: "Not, not, yeah, now I can.

STS-ICOM: McCool: "Now I can see your camera."

STS-ICOM: Husband: "OK." (said as if to tell the crew it's time to start paying attention)

08:47:19 a.m. - STS-ICOM: Clark: "Stop playing."

08:47:20 a.m. - STS-ICOM: Chawla: "I see 22-10. 10-52 is what we were looking for, for...

STS-ICOM: Husband: "OK. 10-16, right? I've got 16 written here."

08:47:32 a.m. - STS-ICOM: McCool: "Yeah, 22 10 16."

STS-ICOM: Chawla: "Yeah, 22 10 16, that's correct. Sorry."

Editor's Note: The ICOM video tape ends at this point.

08:47:38 a.m. - MCC-FDO: "I would concur, we are seeing, we're definitely seeing some spatial differences here. From the STA (shuttle training aircraft) and this morning. I would concur with that."

MCC-FLIGHT: "OK, well yeah, and the STA, the last dive here - and we're not going to have him do any more - was 19 41 (1,941 feet) with close."

MCC-FDO: "Ummm"

08:47:48 a.m. - MCC-Commentator: "Columbia's course toward Florida will take it across the continental United States, crossing the California coast above the San Francisco bay area and continuing across Sacramento, California, providing a spectacular view for persons in that area of Columbia's descent through the atmosphere. That observation of the shuttle would begin about 5:51 a.m. Pacific standard time and continue for about four minutes, until about 5:55 a.m. Pacific time, with the shuttle at an elevation of about 78 degrees."

08:47:52 a.m. - QBAR = 2.0 psf; elevons and body flap active. H=288,932; Mach: 24.66 (+36.398-150.847)

08:47:55 a.m. - MCC-FLIGHT: "He normalized to 19 41 with close."

MCC-FDO: "Yeah..."

MCC-FLIGHT: "Did I get that right?"

MCC-FDO: "X-corrected I heard was 17 84. The X-corrected normalized."

08:48:09 a.m. - MCC-FLIGHT: "Yeah, we're talking about the normalized."

MCC-FDO: "I think the STA performs a correction on top of the normalization to account for, ummm,

MCC-FLIGHT: "Yeah, you're talking XCN, I was just saying the normalized is 19 41."

MCC-FDO: "Yes sir."

08:48:15 a.m. - MCC-Commentator: "It'll be visible as well through much of the United States' southwest above southern Nevada and northern Arizona and central New Mexico as it continues its descent through the atmosphere, trailing a plasma trail left as it heats the atmosphere around it during its descent.

08:48:24 a.m. - MCC-FLIGHT: "OK, what we've got, the last balloon data to come in before we make our decision."

MCC-FDO: "Yes sir."

08:48:39 a.m. - OEX data: Strain gauge sensor G9921, located inside left wing in line with RCC panel No. 9, begins to show an off-nominal increase. This is the first indication of anything amiss aboard Columbia. NEW

08:48:40 a.m. - MCC-Commentator: "Columbia's altitude now 54 miles as it continues to descend into the atmosphere, wings level, nose angled up 40 degrees to control heating. Columbia's traveling about 17,000 miles per hour."

08:48:59 a.m. - OEX data: Temperature sensor 9910, located in front of the left wing spar behind RCC panel No. 9 begins showing an off-nominal increase. This is the first sign of unusual heating. NEW

08:49:07 a.m. - Closed loop guidance initiated. H=259,978; Mach: 24.58 (37.639-144.803)

08:49:16 a.m. - Roll jets deactivated. Qbar equals 10 pounds per square foot. Mach: 24.57

08:49:32 a.m. - Initial roll. Mach 24.51.

08:49:38 a.m. - MCC-GPO: "CLG (closed loop guidance) init."

MCC-FLIGHT: "Copy."

08:49:53 a.m. - OEX data: Temperature sensor 9220, located on the forward side of the left OMS pad, starts an unusual drop. NEW

08:50:03 a.m. - MCC-GPO: "Rolling right."

08:50:00-43 a.m. - Five unexpected return link S-band communications drop outs; upper left aft antenna/TDRS-171 West. Out of family based on comparison with previous Columbia entries from 39-degree inclination orbits to KSC and similar look angles to TDRS West.

08:50:03 a.m. - MCC-Commentator: "Columbia's altitude 48 statute miles as it begins the first in a series of four banks to dissipate speed as it descends into the atmosphere, banking to the right now, a steep bank of 60 degrees and approaching the west coast of the United States. Columbia's speed 16,620 miles per hour, range to touchdown at the Kennedy Space Center runway 3,450 statute miles."

08:50:06 a.m. - STS-?: "garble in static"

08:50:26 a.m. - MCC-MALE VOICE: "I got it."

08:50:30 a.m. - First indication of normal re-entry heating; nominal rise in aft fuselage center bottom line bond temperature sensor (1).

08:50:53 a.m. - Start of peak heating region. H=243,048; Mach: 24.12 (+38.744-136.142)

08:50:56 a.m. - MCC-Commentator: "Columbia in almost an 80-degree-bank to the right to dissipate speed, the first of four banks it performs as it approaches Florida to slow down as it descends. Altitude now 47 miles or about 248,000 feet. The shuttle's speed is 16,400 miles per hour."

08:51:14 a.m. - OEX data: Temperature sensor 9895, located inside the left wing roughly in line with RCC panel No. 9, begins showing an unusual temperature increase. This indicates a plume of hot gas has entered the wing's interior through a breach in the leading edge. NEW

08:51:19/08:52:49 a.m. - A "remote sensor" (Defense Support Program infrared missile early warning satellite) shows an off-nominal plume event. Analysis of data after a communications dropout shows numerous jet firings occurred around this event (L2L, L3L, R2R, R3R). This may be a nominal event. UPDATE

08:51:26 a.m. - MCC-Commentator: "Aboard the shuttle on the flight deck are shuttle commander Rick Husband and pilot Willie McCool, flight engineer Kalpana Chawla and mission specialist Laurel Clark. On the lower deck of the shuttle for entry are payload commander Mike Anderson, mission specialist David Brown and payload specialist, from the Israel space agency, Ilan Ramon."

08:51:46 a.m. - Inertial sideslip angle (beta) goes negative and stays negative until loss of signal; consistent with a negative rolling and yawing torque on the spacecraft.

08:52:05 a.m. - First indication of off-nominal aero increments (delta yawing moment coefficient).

08:52:05 a.m. - MCC-Commentator: "Columbia approaching the Coast of California now, it is predicted to cross the coast and be visible in the San Francisco area about 5:51 a.m. Central time, uh, Pacific standard time rather, and pass almost directly overhead of Sacramento, California. It actually crosses the California coast just to the north of the San Francisco area."

08:52:09-15 a.m. - Sixth unexpected S-band return link comm dropout (event 6). Out of family based on previous flight data.

08:52:15 a.m. - Second indication of normal entry heating; nominal rise in center line bond temperature sensor (2). Mid fuselage "mid" skin temperature; mid fuselage bottom center bond line temperature at x1214.

08:52:17 a.m. - Vehicle location: 300 miles from the California coast. Approximate vehicle location when first off-nominal data recorded. H=236,800; Mach: 23.6 (+39.0-129.2).

08:52:17 a.m. - Left main gear brake temperature D sensor on wheel well sidewall aft of switch valves shows a one "bit flip" change, indicating an increase of about 1.5 degrees. This reading initially was believed to be the first sign of off-nominal heating inside the left wing but it may, in fact, have been normal. NASA research shows at least 13 other missions saw similar bit flips in the same time frame. H=236,791; Mach: 23.58 (+38.993-129.151) UPDATE

08:52:19 a.m. - OEX data: Temperature sensor 9910, located in front of the left wing spar behind RCC panel 9, drops off line after climbing to 50 degrees Fahrenheit. This sensor was insulated and presumably dropped off-scale low when its wiring was damaged or severed by hot gas. NEW

08:52:25-31 a.m. - Unexpected S-band return link comm drop outs (events 7 and 8).

08:52:32 a.m. - Supply water dump nozzle temperature sensors A and B show temporary increase in temperature rise rate (15-second duration), then return to normal profile. Vacuum vent temperature shows temporary increase in rise rate (23 seconds) then returns to normal profile. H=235,602; Mach: 23.47 (+38.974-127.894)

08:52:41 a.m. - Left main gear brake line temperature A sensor on strut facing the main landing gear door begins seeing an off-nominal temperature rise; left main gear brake line temperature sensor C sees off-nominal temperature rise. H=234,928; Mach: 23.40 (+38.995-127.191)

08:52:47 a.m. - Supply water dump nozzle temperature sensors A and B return to normal rise rate.

08:52:49 a.m. - OEX data: Temperature sensor 9895, located inside the left wing behind RCC panel 9, fails after reading 450 degrees. NEW

08:52:49-55 a.m. - Unexpected S-band return link comm dropout (event 9).

08:52:54 a.m. - MCC-Commentator: "Columbia is on target for runway three-three at the Kennedy Space Center Shuttle Landing Facility runway."

08:52:55 a.m. - Vacuum vent temperature sensor returns to normal rise rate.

08:52:56 a.m. - Left inboard elevon lower skin temperature sensors starts an off-nominal trend downward.

08:52:59 a.m. - Left inboard elevon lower skin temperature goes off-scale low (drops off line). H=233,618; Mach: 23.25 (+38.895-125.714)

08:53:00 a.m. - MCC-Commentator: "The subject of runway selection has been discussed in mission control, it continues to be discussed some, but in the meanwhile at present the original targeting for Columbia is toward runway three-three..."

08:53:01 a.m. - First clear indication of an off-nominal rolling moment increment (start of steady negative growth in roll moment.

08:53:02 a.m. - Hydraulic system 1 left inboard elevon actuator return line temperature begins trending down; Hydraulic system 3 left outboard elevon return line temperature sensor begins trending down. H=233,457; Mach: 23.23 (+38.883-125.482)

08:53:09 a.m. - OEX data: Temperature sensor 9220, located on the forward face of the left OMS pod, suddenly reverses an unusual downward trend and begins rising sharply. This sensor ultimately reads 1,200 degrees (normal maximum is about 60 degrees). NEW

08:53:10 a.m. - "... and as it approaches runway three-three, it will perform a right overhead 212-degree turn to align with that runway around the heading alignment cylinder, an imaginary cylinder created by the microwave scan beam landing system at the shuttle runway that assists in the shuttle's guidance toward its final approach to the runway."

08:53:10 a.m. - Hydraulic system 3 left outboard elevon return line temperature sensor drops off-scale low (preceded by nominal temperature rise). H=232,864; Mach: 23.17 (+38.848-124.864)

08:53:11 a.m. - Hydraulic system 1 left inboard elevon actuator return line temperature sensor goes off-scale low (preceded by nominal temperature rise). H=232,793; Mach: 23.16

08:53:15 a.m. - EOC2-4-0064/Fairfield, California: Video coverage begins. (Lat/Lon TBD)

08:53:24 a.m. - Angle of attack modulation active. Nominal event.

08:53:26 a.m. - Columbia crosses the California coastline. H=231,600; Mach: 23.0 (+38.7-123.5)

08:53:29 a.m. - EOC2-4-0056/Lick Observatory, California: Video coverage begins. (+37.342-121.643)

08:53:31-34 a.m. - Hydraulic system 1 left outboard elevon return line temperature drops off-scale low. Preceded by normal temperature rise; data loss three seconds prior to event. H=231,304; Mach: 23.0

08:53:32 a.m. - MCC-Commentator: "Shuttle's altitude now 45 miles, speed 15,800 miles per hour, continuing in a right bank with wings angles 70 degrees, the first of four banks it performs to dissipate speed as it approaches landing."

08:53:32-34 a.m. - Unexpected S-band return link comm drop out (event 10).

08:53:34 a.m. - Third indication of re-entry heating with nominal rise in three center line bond temperature sensors (mid fuselage bottom port bondline temps x620, x777 and forward fuselage lower skin bottom center line).

08:53:34 a.m. - Hydraulic system 2 left inboard elevon return line temperature begins trending down. H=231,077; Mach: 22.97 (+38.707-122.952)

08:53:36 a.m. - Hydraulic system 2 left inboard elevon return line temperature goes off-scale low. H=230,915; Mach 22.95

08:53:36 a.m. - EOC2-4-0026/Sparks, Nevada: Video coverage begins. (+39.541-119.768)

08:53:44-48 a.m. - Debris No. 1: First report of debris observed leaving the orbiter. Seen just behind orbiter envelope. No evidence of RCS thruster firing. H=230,348; Mach: 22.88 (+38.631-122.119)

08:53:45 a.m. - MCC-Commentator: "Columbia crossing the California coast, again, just to the north of the San Francisco area. It's course will take it across Sacramento, California."

08:53:46-50 a.m. - Debris No. 2: Second report of debris observed leaving the orbiter, just aft of the shuttle envelope. No evidence of RCS thruster firing. H-=230,276; Mach: 22.87 (+38.624-122.044)

08:53:46 a.m. - Left main gear brake line temperature A sensor on strut facing main landing gear door begins showing a rise from 1.4 degrees Fahrenheit per minute to 5.5 F/min; increases through loss of signal. H=230,203; Mach: 22.86 (+38.616-121.968)

08:53:54-58 a.m. - Debris No. 3: Third report of debris shedding, directly above Sacramento. Seen just aft of the shuttle. Momentary brightening of plasma trail. No evidence of RCS thruster firings. H=229,621; Mach: 22.79 (+38.554-121.367)

08:54:00-04 a.m. - Debris No. 4: Fourth report of debris shedding just east of Sacramento, seen just aft of the orbiter. No evidence of RCS thruster firings. H=229,113; Mach: 22.73 (+38.496-120.843)

08:54:03 a.m. - EOC2-4-0034/Reno, Nevada: Video coverage begins. (+39.53-119.813)

08:54:07-11 a.m. - Debris No. 5: Fifth report of debris shedding; seen just aft of orbiter envelope. No evidence of RCS thruster firings. H=228,817; Mach: 22.69 (+38.461-120.545)

08:54:10 a.m. - Left main gear brake line temperature B sensor begins showing an off-nominal temperature rise. H=228,460; Mach: 22.64 (+38.416-120.172)

08:54:14-22 a.m. - Unexpected S-band return link comm drop out (event 11).

08:54:15 a.m. - EOC2-4-0009-B/Springfield, California: Video coverage begins. (+36.226-118.805)

08:54:18 a.m. - EOC2-4-0064/Fairfield, California: Video coverage ends. (Lat/Lon TBD; exact LOS time TBD)

08:54:20 a.m. - Start of slow elevon trim change, presumably to counteract the buildup of aerodynamic drag on the left wing. (Time approximate; +/- 10 seconds)

08:54:20 a.m. - Reversal of growth trend in derived roll moment coefficient; moment changes from negative slope to positive.

08:54:22 a.m. - Mid fuselage left bondline temperature sensor at x1215 begins reporting an unusual rise from 1 F/min to 7.6 F/min; Left aft fuselage sidewall temperature sensor at x1410 begins seeing an unusual increase from 2.7 F/min to 5.5 F/min. H=227,560; Mach: 22.52

08:54:24 a.m. - System 3 left main gear strut actuator temperature sensor begins reporting an off-nominal temperature increase. H=227,437; Mach: 22.51 (+38.270-119.068)

08:54:24 a.m. - MCC-MMACS: "Flight, MMACS."

MCC-FLIGHT: "Go ahead, MMACS."

MCC-MMACS: "FYI, I've just lost four separate temperature transducers on the left side of the vehicle, hydraulic return temperatures. Two of them on system one and one in each of systems two and three.

08:54:25 a.m. - Columbia crosses the California-Nevada state line. H=227,400; Mach: 22.5 (+38.3-119.0)

08:54:26 a.m. - S-band comm switched from upper left antenna to upper right antenna. Nominal event.

08:54:28 a.m. - EOC2-4-0056/Lick Observatory, California: Video coverage ends. (+37.342-121.643)

08:54:33 a.m. - EOC2-4-0030/Las Vegas, Nevada: Video coverage begins. (+36.309-115.274)

08:54:33.3-33.9 a.m. - Flash No. 1: Orbiter envelope suddenly brightened for 0.3 seconds, leaving "noticeably luminescent" signature in Columbia's plasma trail. R3R and R2R thrusters fired briefly at 8:54:33.52 and .76 respectively and again at 8:54:33.54 and 78). H=226,894; Mach: 22.43

08:54:35-37 a.m. - Debris No. 6: Sixth report of debris leaving the shuttle; described as "very bright." Orbiter envelope brightened for 0.3 seconds. Debris events 6 and 14 are visually the brightest of all such events over the western United States. H=226,748; Mach: 22.41 (+38.154-118.265)

08:54:41 a.m. - EOC2-4-0017/Flagstaff, Arizona: Video coverage begins. (+35.198-111.651)

08:54:45 a.m. - EOC2-4-0034/Reno, Nevada: Video coverage ends. (+39.53-119.813)

08:54:46 a.m. - MCC-FLIGHT: Four hyd return temps?"

MCC-MMACS: "To the left outboard and left inboard elevon."

MCC-FLIGHT: "OK, is there anything common to them? DSC (discrete signal conditioner) or MDM (multiplexer-demultiplexer) or anything? I mean, you're telling me you lost them all at exactly the same time?"

08:54:49 a.m. - EOC2-4-0026/Sparks, Nevada: Video coverage ends. (+39.541-119.768)

08:54:53 a.m. - Main landing gear left outboard wheel temperature begins off-nominal trend; two bit flips up. H=225,610; Mach: 22.22 (+37.933-116.896)

08:54:58 a.m. - MCC-MMACS: "No, not exactly. They were within probably four or five seconds of each other."

MCC-FLIGHT: "OK, where are those, where is that instrumentation located?

08:55:04-10 a.m. - Debris No. 7: Seventh report of debris leaving the orbiter. No evidence of RCS thruster firings.

08:55:05 a.m. - EOC2-4-0028/St. George, Utah: Video coverage begins. (+37.22-113.622)

08:55:08 a.m. - MCC-MMACS: "All four of them are located in the aft part of the left wing, right in front of the elevons, elevon actuators. And there is no commonality."

08:55:11 a.m. - EOC2-4-0009-B/Springfield, California: Video coverage ends. (+36.226-118.805)

08:55:11 a.m. - EOC2-04-0021/St. George, Utah: Video coverage begins. (+37.591-115.059)

08:55:12 a.m. - System 3 left main landing gear brake sidewall valve return line temperature (forward) begins trending up. H=224,546; Mach: 22.02 (+37.674-115.479)

08:55:18 a.m. - MCC-FLIGHT: "No commonality."

08:55:21 a.m. - Drag is recorded at 11 feet per second squared. Flight control system begins incorporating drag measurements. Nominal event. H=224,002; Mach: 21.92 (37.535-114.781)

08:55:21-27 a.m. - Debris No. 8: Eighth report of debris leaving the shuttle; plasma trail momentarily brightens. No evidence of RCS thruster firings.

08:55:23 a.m. - EOC2-4-0005/Ivins, Utah: Video coverage begins. (+37.169-113.679)

08:55:25-29 a.m. - Debris No. 9: Ninth report of debris leaving the shuttle; event followed by multiple secondary plasma trails. No evidence of RCS thruster firings.

08:55:26-30 a.m. - Debris No. 10: Tenth report of debris leaving the orbiter; seen well aft of orbiter envelop. No evidence of RCS thruster firings.

08:55:30 a.m. - EOC2-04-0050/St. George, Utah: Video coverage begins. (+37.591-115.059)

08:55:30 a.m. - External sensors record an "off-nominal event." Time is approximate, but there is a preliminary match with debris No. 10. Strong confidence this is an off-nominal event. In response to a query, NASA replied: "The DOD utilizes sensors from a wide variety of resources, including satellites, radar, etc., and this 'event' was discerned from a combination of those resources. The data is not conclusive enough to distinguish whether the 'off nominal external event' is something being shed or plume, but does indicate something not seen on previous flights."

08:55:32 a.m. - Columbia crosses the Nevada-Utah state line. H=223,400; Mach: 21.8 (+37.4-114.1)

08:55:33-35 a.m. - S-band return link comm dropout (event 12); first drop out after antenna switch to upper right aft antenna; inconclusive if this is off nominal.

08:55:36-42 a.m. - Debris No. 11: Eleventh report of debris leaving the orbiter; seen well aft of orbiter envelope. No evidence of RCS thruster firings.

08:55:38 a.m. - MCC-Commentator: "Columbia continuing in a right bank, the wings angled 43 degrees, speed 15,000 miles per hour, altitude 43 miles, 2,090 miles to touchdown at the Kennedy Space Center targeted for runway three-three at Kennedy at present. Crossing the continental United States, now crossing above southern Nevada to the north of Las Vegas."

08:55:41 a.m. - Mid fuselage port sill longeron temperature at x1215 detects an unusually high increase, from 0 F/min to 2.6 F/min. H=222,821; Mach: 21.69 (+37.238-113.405)

08:55:45-49 a.m. - Debris No. 12: Twelfth report of debris leaving the orbiter; event was preceded and followed by secondary plasma trails. No evidence of RCS thruster firings.

08:55:49 a.m. - Columbia moves into sunlight from orbital darkness. (+37.096-112.795)

08:55:54 a.m. - EOC2-04-0050/St. George, Utah: Video coverage ends. (+37.591-115.059)

08:55:55 a.m. - Columbia crosses the Utah-Arizona state line. H=222,100; Mach: 21.5 (+37.0-112.4)

08:55:55-59 a.m. - Debris No. 13: Thirteenth report of debris leaving the orbiter; event was followed by a brief brightening of the plasma trail adjacent to debris. No evidence of RCS thruster firings.

08:55:57 a.m. - EOC2-4-0030/Las Vegas, Nevada: Video coverage ends. (+36.309-115.274)

08:55:58-00 a.m. - Debris No. 14: Fourteenth report of debris leaving the orbiter; seen just aft of orbiter envelope. Debris 6 and 14 are visually the brightest debris events seen.

08:56:00-03 a.m. - S-band return link comm dropout (event 13); on upper right aft antenna; not clear if this is off nominal.

08:56:02 a.m. - Aerodynamic pressure (Qbar) is 40 pounds per square foot. Aft reaction control system pitch jets are deactivated. H=221,670; Mach: 21.45 (+36.883-111.924)

08:56:02 a.m. - MCC-FLIGHT: "MMACS, tell me again which systems they're for."

MCC-MMACS: "That's all three hydraulic systems. It's... two of them are to the left outboard elevon and two of them to the left inboard.

08:56:03 a.m. - Left lower wing skin temperature begins trending down due to possible sensor or wiring damage. H=221,612; Mach: 21.44 (+36.866-111.858)

08:56:06 a.m. - EOC2-4-0028/St. George, Utah: Video coverage ends. (+37.767-115.972)

08:56:09-13 a.m. - Debris No. 15: Fifteenth report of debris leaving the orbiter; seen just aft of orbiter envelope. RCS thruster R2R fired briefly at 8:56:17 and :54 and R3R fired briefly at 8:56:17 and :52.

08:56:10 a.m. - EOC2-4-0005/Ivins, Utah: Video coverage ends. (+37.169-113.679)

08:56:12 a.m. - MCC-FLIGHT: "OK, I got you.

MCC-GNC: "Flight, guidance, we're processing drag with good residual."

MCC-FLIGHT: "Copy. Thank you."

08:56:16 a.m. - Hydraulic system 1 left main gear uplock actuator unlock line temperature increases from 0.7 F/min to 3.9 F/min; increases through LOS. H=220,778; Mach: 21.28 (+36.625-110.936)

08:56:17 a.m. - System 3 left main gear brake switch valve return line temperature (forward) sees an increase from 1.5 F/min to 8.8 F/min; remains constant to LOS. H=220,711; Mach: 21.27 (+36.607-110.871)

08:56:17 a.m. - EOC2-04-0021/St. George, Utah: Video coverage ends. (+37.591-115.059)

08:56:20 a.m. - Left main gear brake line temperature C sensor sees change from 1.3 F/min to 9.9 F/min; remains constant to LOS. H=220,488; Mach: 21.23 (36.554-110.676)

08:56:22 a.m. - Left main gear brake line temperature B sensor sees a rise rate change from 2.1 F/min to 9.1 F/min; continues increasing through LOS. H=220,374; mach: 21.21 (+36.518-110.546)

08:56:24 a.m. - Left upper wing skin temperature sensor sees start of off-nominal trend downward due to possible sensor or wiring damage). H=220,235; Mach: 21.17 (+36.482-110.417)

08:56:30 a.m. - Columbia begins the first of four banking maneuvers called roll reversals to bleed off energy. H=219,820; Mach: 21.13

08:56:39 a.m. - MCC-GC: "Flight, GC."

MCC-FLIGHT: "Go."

MCC-GC: "Your air-to-grounds are enabled for the landing count."

MCC-FLIGHT: "Thank you."

08:56:45 a.m. - Columbia crosses the Arizona-New Mexico state line. H=219,000; Mach: 20.9 (+36.1-109.0)

08:56:49 a.m. - MCC-Commentator: "Columbia's course continuing across Arizona and the Arizona and New Mexico border near the four corners area of the United States. Its course will take it almost directly above Albuquerque, New Mexico, it's altitude now 225,000 feet or 42 miles, speed 14,300 miles per hour, 1,785 miles to touchdown at the Kennedy Space Center.

08:56:53 a.m. - System 3 left main gear strut actuator temperature sees increase from 1.7 F/min to 12.9 F/min; remains constant through LOS. H=218,839; Mach: 20.80

08:56:55 a.m. - First roll reversal complete. H=218,817; Mach: 20.76

08:56:55-57 a.m. - S-band return link comm dropout (event 14). May not be off nominal. This is the final potentially off-nominal comm event.

08:56:58 a.m. - Inertial measurement unit (IMU) velocity increase; considered a normal signature due to accelerations imparted by roll reversal. H=218,784; Mach: 20.74

08:57:XX a.m. - Body flap deflected upward 3 degrees; considered nominal (exact time TBD).

08:57:11 a.m. - MCC-Commentator: It's banking now back to the left, the second in a series of four banks that dissipate speed of the spacecraft as it becomes an aircraft and descends into the atmosphere toward Florida. Wings angled about 75 degrees to the left."

08:57:19-29 a.m. - Debris No. 16. Very faint debris observed leaving the orbiter. Observations by observers at Kirtland AFB Starfire Optical Range; numerous jet firings inferred from injector temperatures.

08:57:19 a.m. - Main landing gear left outboard tire pressure 1 begins an off-nominal trend (bit flip up). H=217,757; Mach: 20.45 (+35.385-106.785)

08:57:24 a.m. - Main landing gear left outboard tire pressure 2 begins an off-nominal trend (bit flip up). H=217,315; Mach: 20.38 (+35.290-106.481)

08:57:25 a.m. - MCC-FLIGHT: "GNC, FLIGHT."

MCC-GNC: "FLIGHT, GNC."

MCC-FLIGHT: "Everything look good to you, control and rates and everything is nominal, right?"

08:57:28 a.m. - Left lower wing skin temperature drops off-scale low (sensor failure). H=216,845; Mach: 20.31 (+35.215-106.239)

08:57:31 a.m. - EOC2-4-0017/Flagstaff, Arizona: Video coverage ends. (+35.198-111.651)

08:57:35 a.m. - MCC-GNC: "Control's been stable through the rolls that we've done so far, flight. We have good trims. I don't see anything out of the ordinary."

08:57:43 a.m. - Left upper wing skin temperature sensor drops off-scale low. H=215,020; Mach: 20.09

08:57:45 a.m. - MCC-FLIGHT: "OK. And MMACS, FLIGHT?"

MCC-MMACS: "FLIGHT, MMACS."

MCC-FLIGHT: "All other indications for your hydraulic system indications are good."

08:57:53 a.m. - MCC-MMACS: "They're all good. We've had good quantities all the way across."

MCC-FLIGHT: "And the other temps are normal?"

MCC-MMACS: "The other temps are normal, yes sir."

08:57:53.7 a.m. - Flare 1: Asymmetrical brightening of orbiter shape over New Mexico. Observed by Starfire Optical Range personnel. Numerous rocket firings.

08:57:54 a.m. - System 2 left brake switch valve return temperature (aft) begins seeing an off-nominal temperature increase. H=213,270; mach: 19.91

08:57:59 a.m. - MCC-FLIGHT: "And when you say you lost these, are you saying that they went to zero..."

MCC-MMACS: "All four of them are off-scale low."

MCC-FLIGHT: "... or off-scale low."

MCC-MMACS: "And they were all staggered. They were, like I said, within several seconds of each other."

MCC-FLIGHT: "OK."

08:57:59.5-01.5 a.m. - Flare 2: Asymmetrical brightening of orbiter shape over New Mexico. Observed by Starfire Optical Range personnel. Numerous rocket firings.

08:58:03 a.m. - Start of "sharp" elevon trim increase to counteract increasing aerodynamic drag (timing +/- 10 seconds). H=212,007; Mach: 19.79

08:58:09 a.m. - Substantial increase in calculated rolling and yawing moments.

08:58:16 a.m. - Left main gear brake line temperature sensor D sees a rise rate change from 0.9 F/min to 11.7 F/min (not increasing) to LOS. H=210,304; Mach: 19.55 (+34.287-103.293)

08:58:20 a.m. - Columbia crosses the New Mexico-Texas state line. H=209,800; Mach: 19.5 (+34.2-103.1)

08:58:32 a.m. - Main landing gear left outboard/inboard tire pressure 1 sensors see pressure trending down to off-scale low; main landing gear left outboard wheel temperature begins trending down to off-scale low (timing not exact; follows 7-second loss of signal)

08:58:32-22 a.m. - System 2 left brake switching valve return temperature (aft) sees rise from 2.5 F/min to 40 F/min until peak at 8:59:22 a.m. H=208,380; Mach: 19.28 (+33.980-102.325)

08:58:36 a.m. - Main landing gear inboard wheel temperature begins trending down to off-scale low. H =207,918; Mach: 19.21 (+33.908-102.099)

08:58:36 a.m. - MCC-Commentator: "Columbia continuing toward Florida, now approaching the New Mexico-Texas border. Altitude 40 miles..."

08:58:38 a.m. - Main landing gear outboard tire pressure 1 sensor drops off-scale low.

08:58:39 a.m. - Main landing gear left outboard wheel temperature goes off-scale low; main landing gear left outboard tire pressure 2 sensor begins trending down to off-scale low. (+33.873-101.987)

08:58:40 a.m. - Columbia's backup flight system (BFS) computer displays four tire pressure fault messages on a cockpit display.

08:58:40 a.m. - Main landing gear inboard tire pressure 1 sensor drops off-scale low. H=207,370; Mach: 19.13 (+33.837-101.875)

08:58:41 a.m. - Main landing gear left inboard tire pressure 2 sensor stars off-nominal increase, rising about 3.5 psia in 2 seconds. H=207,132; Mach: 19.09

08:58:43 a.m. - Main landing gear inboard tire pressure 2 begins trending down.

08:58:44 a.m. - MCC-FDO: "FLIGHT, FDO."

08:58:48 a.m. - STS-CDR: "And, uh, Hou(ston)..."

08:58:48 a.m. - Main landing gear left inboard wheel temperature and main landing gear inboard tire pressure 2 sensors drop off-scale low. H=206,403; Mach: 18.99

08:58:51 a.m. - MCC-Commentator: "... speed 13,200 miles per hour. Range to touchdown 1,400 miles. The shuttle in a left bank with the wings banked about 57 degrees to horizontal."

08:58:54 a.m. - Main landing gear left outboard tire pressure 2 sensor drops off-scale low. H=205,553; Mach: 18.86

08:58:56 a.m. - Backup flight system computer displays tire pressure fault message (final message). H=205,311; Mach: 18.83 (+33.541-100.931)

08:59:06 a.m. - MCC-FLIGHT: "FDO, FLIGHT."

MCC-FDO: "Uh, we have the balloon. It is being run through DDS (data display system) right now."

08:59:06 a.m. - Left main gear downlocked indication - transferred ON - uplock indicates no change. H=204,336; Mach: 18.86 (+33.370-100.384)

08:59:15 a.m. - MCC-MMACS: "FLIGHT, MMACS."

MCC-FLIGHT: "Go."

08:59:18 a.m. - MCC-MMACS: "We just lost tire pressure on the left outboard and left inboard, both tires."

08:59:22 a.m. - System 2 left brake switching valve return temperature sensor (aft) begins a sharp downward trend to off-scale low.

08:59:23 a.m. - Loss of realtime data in mission control workstations.

08:59:24 a.m. - MCC-CAPCOM: "And Columbia, Houston, we see your tire pressure...

MCC-FLIGHT: "Copy..."

MCC-CAPCOM: "...messages and we did not..."

MCC-FLIGHT: "Is it instrumentation, MMACS? Gotta be..."

MCC-CAPCOM: "...copy your last."

08:59:30.66 a.m. - Start of R2R yaw jet firing; jets on at loss of signal to assist elevons in counteracting the increasing aerodynamic drag. H=200,767; Mach: 18.16 (+32.956-99.041)

08:59:30.68 a.m. - Start of R3R yaw jet firing; jet on at loss of signal to assist elevons in counteracting the increasing aerodynamic drag.

08:59:30 a.m. - MCC-MMACS: "FLIGHT, MMACS, those are...

08:59:31 a.m. - Maximum observed elevon deflections; Left: -8.11 degrees up; Right: -1.15 degrees up

08:59:31.4 a.m. - Flight control system channel 4 aerosurface position measurements start trending toward their null values. This indicates worsening failures and wiring shorts.

08:59:31.478 a.m. - All flight control system channel 4 bypass valves close (indicate bypass). This is an indication of ASA high-rate data failure.

08:59:31.7 a.m. - Speedbrake channel 4 OI position measurement indicates 19, 20 and 24 degrees open over last three samples prior to loss of signal. Speedbrake should be closed at 0 degrees. No change seen in actuator motion. Signature considered nominal response to bypass valve closing (see above).

08:59:32 a.m. - Maximum observed elevon trim (-2.3 degrees); loss of signal for left mid fuselage bondline temperature sensor at x1215; left aft fuselage sidewall temperature at x1410; left main gear brake line temperatures (A: 172.2 F; B: 154.2 F; C: 104.8 F; D: 88.3 F); left main gear strut actuator temperature (76.3 F); hydraulic system 1 left main gear uplock actuator unlock line temperature (52.2 F); System 2 left brake switch valve return temperature (aft, 62.8 F); system 3 left main gear brake switch valve return line temperature (67.3 F)

08:59:32 a.m. - Columbia is approaching Dallas, Texas. Approximate location at initial loss of signal. H=200,700; Mach: 18.1 (+32.9-99.0)

08:59:32 a.m. - STS-CDR: "Roger, uh buh (CUTOFF)" (Editor's note: Phonetically, sounded like first syllable of "before" or possibly "both;" he may have been responding to the BFS fault messages for both left-side main landing gear tires)

MCC-MMACS: "...also off-scale low."

08:59:32.130 a.m. - Flight control system channel 4 fail flags raised on all aerosurface actuators.

08:59:32.136 a.m. - Last valid data frame accepted by ODRC - OI/BFS/PASS. The backup flight system computer selected the upper right aft quad antenna to communicate with TDRS-West. The pointing angle was off the shuttle's tail at -65 degrees and trending further into blockage; previous experience shows a probable loss of communications at angles greater than -60 degrees. Therefore, the loss of communications experienced here is consider normal and not the result of any failure or attitude change by the orbiter.

08:59:32.195 a.m. - ASA 4 remote power controller and A&C trip indication due to electrical short.

08:59:33.598 a.m. - Left outboard bypass valve reopens. A "force fight" between channels 1/2/3/4 begins, resulting in a difference of up to 0.5 degrees between left outboard and inboard elevons; indicates a short in the bypass valve.

08:59:33.680 a.m. - Backup flight system fault message (1): Flight control system Channel 4 (TDRS-East data). Error is detected by ATVC/ASA hardware when sensed change in pressure across the actuator exceeds a limit indicating the FCS channel is no longer driving the actuator.

08:59:33.863 a.m. - PASS flight computers annunciate a fault (1): Flight control system channel 4 (TDRS-East data).

08:59:33.976 a.m. - Master alarm sounds in the cockpit; cause as yet unknown.

08:59:34.518 a.m. - Left outboard "force fight" ends; driver currents go to zero, indicating remote power controller B has tripped; all bypass valves would open.

08:59:34.561 a.m. - Speed brake force fight begins and continues to LOS; indicates opening of all bypass valves due to RPC B trip on ASA 4. Speedbrake is already at zero.

08:59:35-36 a.m. - Vehicle sideslip changes sign. Just prior to initial LOS, the magnitude of Columbia's negative sideslip start to decrease; Between 8:59:34 and 8:59:37, sideslip grew from -.6 to +.8 degrees. Aerodynamic forces due to sideslip are now reinforcing the drag caused by problems with the left wing.

08:59:36 a.m. - Bank attitude error begins growing. Up until this moment, the flight control system had been able to maintain a bank angle error around 5 degrees. Aerojet DAP (digital autopilot) drops the left wing to compensate for increasing drag, creating a bank attitude error.

08:59:36.8 a.m. - Aerojet DAP commands a third RCS jet - R4R - to fire to counteract increasing aerodynamic forces pulling vehicle to the left (yaw down relative to Earth); R4R fires and remains on through 8:59:37.396 a.m. when data is lost for 25 seconds.

08:59:37 a.m. - Begin hypothetical trajectory plot for an object with a ballistic number = 220 psf. This trajectory is projected to compute an approximate impact point.

08:59:37.3 a.m. - Aerojet DAP orders R1R to begin firing; stays on through LOS at 8:59:37.396 a.m.

08:59:37.X a.m. - Last aileron data; rate of change had reached maximum allowed by flight control system.

08:59:37.396 a.m. - Loss of data for 25 seconds. Additional data in this 25-second gap is recovered in computer buffers during a final two second burst of telemetry.

08:59:46.347 a.m. - PASS flight computers generate a "roll reference" fault message. This message is recovered during final two seconds of telemetry in a computer buffer. The timing of this message - 10 seconds after four aft jets began firing - indicates rapid change in lift-to-drag ratio. BFS does not have this message in the fault message stack. It is likely the BFS annunciated this message during the 25-second LOS.

08:59:49 a.m. - STATIC.

08:59:52.114 a.m. - PASS fault message: Left RCS leak; found in PASS fault message buffer (data suspect).

08:59:58 a.m. - MCC-INCO: "FLIGHT, INCO."

MCC-FLIGHT: "Go."

MCC-INCO: "Just taking a few hits here. We're right up on top of the tail. Not too bad."

08:59:59 a.m. - EOC2-4-0018/Duncanville, Texas: Video coverage begins. (+32.653-96.908)

09:00:00 a.m. - EOC2-4-0024/Arlington, Texas: Video coverage begins. (+32.736-97.108)

09:00:01.540 a.m. - BFS fault message: Left RCS leak; found in BFS fault message buffer (data, timing suspect).

09:00:01.9 a.m. - BFS fault message: Left RCS leak; found in BFS fault message buffer (data, timing suspect).

09:00:02-06 a.m. - Debris A - large piece - seen leaving the orbiter and falling away.

09:00:02.654 a.m. - BFS fault message: Left RCS LJET (data suspect).

09:00:02.660 a.m. - Telemetry resumes for approximately two seconds after a 25-second drop out. Data from this final burst is suspect because of multiple bit errors. Only one data sample was available for many measurements. As a result, some of the following conclusions may be in error.

NOMINAL SYSTEMS: Columbia's APUs were running and the water spray boilers were providing cooling. The main propulsion system (aft engine compartment) was intact. The shuttle's electricity producing fuel cells were generating power and the fuel cell hydrogen/oxygen distribution lines were intact. Communications and navigation systems in the forward fuselage were performing normally. RSB, body flap, main engine and right wing temperature sensors appeared active. The flash evaporator system had shut down. Life support systems were operating normally.

OFF-NOMINAL SYSTEMS: All three hydraulic systems showed zero pressure and empty reservoirs. The left inboard and outboard elevon actuator temperatures were either off-scale low or show now data. The water spray boilers appeared to be over cooling the APU lubrication oil. The flash evaporator cooling system was in shutdown. The majority of the left orbital maneuvering system pod sensors were either off-scale low or showing no data. Multiple BFS and PASS fault messages for left OMS pod hardware were found in buffers. High temperatures at the bottom bondline centerline skin forward and aft of the wheel wells and at the port side structure over the left wing were seen. A general upward shift in main bus amps and downward shift in main bus volts was observed. AC3 phase A inverter appeared disconnected from the AC bus.

SHUTTLE ATTITUDE: Guidance and navigation data suggests Columbia was in an uncommanded orientation, or attitude, and was exhibiting uncontrolled rates of motion. Yaw rate was at sensor maximum of 20 degrees per second, suggesting a possible tumble to the left. Because Columbia was in a left bank at the time, a yaw to the left would have had the effect of dropping the nose toward Earth. Flight control mode was in AUTO, meaning the pilots never took over manual control. But they may have been making an attempt (see below). At this point, it appears the forward, mid and aft fuselage, the right wing and right OMS pod were still intact.

09:00:03.470 a.m. - BFS fault message: Left OMS tank pressure; found in BFS fault buffer. Fault is annunciated when OMS oxidizer or fuel tanks show pressures out of limits high or low (data suspect).

09:00:0X.XXX a.m. - BFS fault message: Unknown (timing unclear).

09:00:0X.XXX a.m. - BFS fault message: SM1 AC VOLTS. Occurred after left OMS tank pressure message (time info corrupted). Error message indicates AC bus 3 phase A, B or C voltage is out of limits high or low.

09:00:03.637 a.m. - PASS fault message: Left RCS PVT (data suspect).

09:00:03.637 a.m. - PASS fault message: Digital autopilot downmode rotational hand controller. Because of software timing issues, this event could have occurred as early as 9:00:01.717 a.m. Fault message corroborated by an initialization flag for the Aerojet DAP roll stick function. However, during this two-second period, rotational hand controller remains centered (in detent) and DAP remains in AUTO through loss of signal. Data is potentially error prone.

09:00:04.826 a.m. - Last identifiable OI downlink frame.

09:00:13.4 a.m. - OEX data: PCM (pulse code modulation) data ends. NEW

09:00:17-21 a.m. - Debris B observed leaving the orbiter.

09:00:18 a.m. - MCC-FLIGHT: "MMACS, FLIGHT."

09:00:18-22 a.m. - Debris C observed well aft of orbiter.

09:00:19.4 a.m. - OEX data: FDM (frequency division multiplexer) data ends. Prior to this moment, the fuselage was still intact and power was still flowing from Columbia's fuel cells. NEW

09:00:21 a.m. - EOC2-4-0025/Camp Swift, Texas: Video coverage begins. (+30.191-97.292)

09:00:21-25 a.m. - Onset of vehicle main body breakup.

MCC-MMACS: "FLIGHT, MMACS."

MCC-FLIGHT: "And there's no commonality between all these tire pressure instrumentations and the hydraulic return instrumentations."

09:00:23 a.m. - EOC2-4-0024/Arlington, Texas: Video coverage ends. (+32.736-97.108)

09:00:27 a.m. - MCC-MMACS: "No sir, there's not. We've also lost the nose gear down talkback and the right main gear down talkback."

MCC-FLIGHT: "Nose gear and right main gear down talkbacks?"

MCC-MMACS: "Yes sir."

09:00:30 a.m. - Time-stamped video from Apache helicopters flying near Fort Hood, Texas, shows multiple contrails.

09:00:32 a.m. - RV2/Fort Hood, Texas: Video coverage begins. (+31.117-97.728)

09:00:35 a.m. - EOC2-4-0018/Duncanville, Texas: Video coverage ends. (+32.653-96.908)

09:00:51 a.m. - MCC-EECOM: "And FLIGHT, EECOM."

MCC-FLIGHT: "EECOM."

MCC-EECOM: "I've got four temperature sensors on the bond line data that are off-scale low."

09:00:53 a.m. - End of peak heating region.

09:01:01 a.m. - EOC2-4-0025/Camp Swift, Texas: Video coverage ends. (+30.191-97.292)

09:01:16 a.m. - MCC-Commentator: "Columbia out of communications at present with mission control as it continues its course toward Florida..."

09:01:19 a.m. - RV2/Fort Hood, Texas: Video coverage ends. (+31.117-97.728)

09:01:29 a.m. - MCC-INCO: "FLIGHT, INCO, I didn't expect, uh, this bad of a hit on comm."

09:01:38 a.m. - MCC-FLIGHT: "GC, how far are we from UHF? Is that two-minute clock good?"

MCC-UNKNOWN: "Affirmative, FLIGHT."

09:02:00 a.m. - MCC-GNC: "FLIGHT, GNC."

MCC-FLIGHT: "Go."

MCC-GNC: "If we have any reason to suspect any sort of controllability issue, I would keep the control cards handy on page four-dash-13."

MCC-FLIGHT: "Copy."

09:02:21 a.m. - MCC-Commentator: "Fourteen minutes to touchdown for Columbia at the Kennedy Space Center. Flight controllers are continuing to stand by to regain communications with the spacecraft..."

09:02:29 a.m. - MCC-FLIGHT: "INCO, we were rolled left last data we had and you were expecting a little bit of ratty comm, but not this long?"

09:02:37 a.m. - MCC-INCO: "That's correct, FLIGHT. I expected it to be a little intermittent. And this is pretty solid right here."

MCC-FLIGHT: "No onboard system config changes right before we lost data?"

MCC-INCO: "That is correct, flight. All looked good."

MCC-FLIGHT: "Still on string two and everything looked good?"

MCC-INCO: "String two looking good."

09:03:03 a.m. - MCC-GC: "Two minutes to MILA."

09:03:12 a.m. - MCC-CAPCOM: "Columbia, Houston, comm check."

09:03:23 a.m. - MCC-FDO: "FLIGHT, FDO."

MCC-FLIGHT: "Go."

MCC-FDO: "Close-end aim point with the one-hour balloon shows us touching down at 1,496, 1,500 feet down the runway. Our crosswind right now is on the left, from the left on the three-three end."

09:03:34 a.m. - Reference trajectory ground impact in western Louisiana for hypothetical object with a ballistic number = 220 psf. (+30.781-92.557)

09:03:40 a.m. - MCC-CAPCOM: "Columbia, Houston, UHF comm check."

09:03:45 a.m. - MCC-Commentator: "CAPCOM Charlie Hobaugh calling Columbia on a UHF frequency as it approaches the Merritt Island tracking station range in Florida. Twelve-and-a-half minutes to touchdown, according to clocks in mission control." (listeners hear unease in the voice inflection)

09:03:46 a.m. - MCC-FDO: "FLIGHT, I'd like to stay where we're at."

MCC-FLIGHT: "I copy."

09:03:53 a.m. - MCC-MMACS: "FLIGHT, MMACS."

MCC-FLIGHT: "MMACS?"

MCC-MMACS: "On the tire pressures, we did see them go erratic for a little bit before they went away, so I do believe it's instrumentation."

MCC-FLIGHT: "OK."

09:04:05 a.m. - MCC-CAPCOM: "Columbia, Houston, UHF comm check."

09:04:35 a.m. - MCC-FDO: "FLIGHT, FDO."

MCC-FLIGHT: "Go."

MCC-MALE VOICE: "I know this data's a little late, the one-hour balloon protects us for winds...

09:04:41 a.m. - MCC-CAPCOM: "Columbia, Houston, UHF comm check."

MCC-FDO: "...I think we're in a smaller wind persistence case than that. In other words, we shouldn't expect as big of a change. I'm comfortable with 1,500 feet down the runway."

09:04:54 a.m. - MCC-Commentator: "Flight controllers are standing by for Columbia to move within communications range of the Merritt Island tracking station in Florida to regain communications with Columbia."

09:04:57 a.m. - MCC-GC: "Flight, GC."

MCC-FLIGHT: "Go."

MCC-GC: "MILA not reporting any RF at this time."

MCC-INCO: "FLIGHT, INCO, SPC just should have taken us to STDN low."

MCC-FLIGHT: "OK."

09:05:13 a.m. - MCC-FLIGHT: "FDO, when are you expecting tracking?"

MCC-FDO: "One minute ago, FLIGHT."

09:05:21 a.m. - MCC-Commentator: "Also, flight controllers standing by for tracking data of Columbia that's also received through the Merritt Island tracking station."

09:05:26 a.m. - MCC-CAPCOM: "Columbia, Houston, UHF comm check."

09:05:51 a.m. - MCC-Commentator: "Ten and a half minutes to anticipated touchdown for Columbia." (voice inflection signals uncertainty)

09:06:29 a.m. - MCC-GC: "And FLIGHT, GC, no C-band yet."

MCC-FLIGHT: "Copy."

09:06:56 a.m. - MCC-Commentator: "Flight controllers are still standing by for C-band tracking data from the Merritt Island tracking station of Columbia and UHF communications."

09:07:08 a.m. - MCC-CAPCOM: "Columbia, Houston, UHF comm check."

09:07:22 a.m. - MCC-INCO: "FLIGHT, INCO."

MCC-FLIGHT: "Go."

MCC-INCO: "I could swap strings in the blind."

09:07:36 a.m. - MCC-FLIGHT: "OK, command us over."

MCC-INCO: "In work, FLIGHT."

09:08:07 a.m. - MCC-Commentator: "Eight minutes on the touchdown clock for Columbia, flight controllers continuing to stand by to regain communications with the spacecraft."

09:08:25 a.m. - MCC-INCO: "FLIGHT, INCO, I've commanded string one in the blind."

MCC-FLIGHT: "INCO?"

MCC-INCO: "I've commanded string one in the blind, FLIGHT."

MCC-FLIGHT: "Copy."

09:08:34 a.m. - MCC-Commentator: "Flight controllers standing by for communications through the Merritt Island tracking station, a ground tracking site in Florida."

09:09:27 a.m. - MCC-GC: "And FLIGHT, GC."

MCC-FLIGHT: "Go."

MCC-GC: "MILA's taking one of their antennas off into a search mode."

MCC-FLIGHT: "Copy. FDO, FLIGHT?"

MCC-FDO: "Go ahead, FLIGHT."

MCC-FLIGHT: "Did we get, have we gotten any tracking data?"

MCC-FDO: "We got a blip of tracking data, it was a bad data point, FLIGHT. We do not believe that was the orbiter. We're entering a search pattern with our C-bands at this time. We do not have any valid data at this time."

09:09:29 a.m. - Projected time Columbia's velocity would have dropped to Mach 2.5 had this been a normal approach.

09:09:55 a.m. - MCC-FLIGHT: "OK. Any other trackers that we can go to?"

MCC-FDO: "Let me start talking, FLIGHT, to my navigator."

09:10:07 a.m. - MCC-Commentator: "This is mission control, Houston. Flight controllers are continuing to seek tracking data of Columbia. Touchdown clocks countdown to six minutes to touchdown for the anticipated shutdown, touchdown of Columbia at the Kennedy Space Center runway. Tracking data is being sought through the Merritt Island tracking station located near the Kennedy Space Center in Florida."

09:10:35 a.m. - MCC-Commentator: "Communications with Columbia were lost at about 8 a.m. Central time, about 10 minutes ago."

09:11:38 a.m. - Projected time Columbia's velocity would have dropped below the speed of sound had this been a normal approach.

09:12:34 a.m. - MCC-Commentator: "This is mission control, Houston. Flight controllers are continuing to stand by for communications from Columbia. The last communications with the spacecraft occurred about 8 a.m. Central time as it was above central Texas. Currently seeking communications or tracking data from the spacecraft through C-band radar and ground tracking sites located at the Merritt Island tracking station in Florida."

09:12:39 a.m. - Projected time Columbia would have been banking on the heading alignment cylinder to line up on runway 33 had this been a normal approach.

09:12:40 a.m. - (time approximate) Mission operations representative Phil Engelauf, sitting directly behind Cain, gets a call informing him that video shot by a Dallas TV station shows multiple contrails along Columbia's path. This is the first notification of vehicle breakup in mission control. Engelauf informs astronaut Ellen Ochoa, sitting to his right, and then Cain. The flight director pauses a moment, digesting the news, and then turns back to the flight control team to declare a contingency.

09:12:55 a.m. - MCC-FLIGHT: "GC, FLIGHT. GC, FLIGHT."'

MCC-GC: "FLIGHT, GC."

MCC-FLIGHT: "Lock the doors."

MCC-GC: "Copy."

09:13:17 a.m. - MCC-FLIGHT: "FDO, do you have any tracking?"

MCC-FDO: "No sir."

09:13:43 a.m. - MCC-MOD: "FLIGHT, MOD, on the flight loop."

09:13:51 a.m. - MCC-FDO: "FLIGHT, FDO."

MCC-FLIGHT: "Go."

MCC-FDO: "My C-bands have not acquired anything. We are only in track, uh, acquiring false locks at this time."

09:14:11 a.m. - MCC-FLIGHT: "I copy, FDO."

09:14:26 a.m. - MCC-Commentator: "This is mission control, Houston. Flight controllers continue to seek tracking or communications with Columbia through Merritt Island tracking station. Last communications with Columbia was at 8 a.m. Central time, approximately above Texas as it approached the Kennedy Space Center for its landing. Flight director Leroy Cain is now instructing controllers to get out their contingency procedures and begin to follow those."

09:14:29 a.m. - MCC-FLIGHT: "OK, all flight controllers on the flight loop, we need to kick off the FCOH (Flight Control Operations Handbook) contingency plan procedure, FCOH checklist page 2.8-5."

09:14:52 a.m. - MCC-FLIGHT: "FDO, FLIGHT. ... FDO, FLIGHT."

MCC-FDO: "Go ahead."

MCC-FLIGHT: "Do you have any information or reports from Space Command?"

09:15:04 a.m. - MCC-Commentator: "Flight dynamics officer reports no tracking data from the C-band radar at the Merritt Island tracking station has been reported of any objects."

09:15:50 a.m. - Columbia's scheduled touchdown time on runway 33 at the Kennedy Space Center.

09:17:57 a.m. - MCC-FLIGHT "OK, all flight controllers, on page 9, of the FCOH procedure you need to make sure you step through the actions required in step 20, that's for your workstation logs, display printouts, there's a whole list of data collection items we need to make sure we log through."

09:18:20 a.m. - MCC-Commentator: "This is mission control, Houston. Flight director Leroy Cain is instructing controllers to follow contingency procedures. The last communications with the shuttle Columbia during its descent from orbit were at about 8 a.m. Central time as it was descending through the atmosphere..."

09:18:36 a.m. - MCC-FLIGHT: "And GC, FLIGHT?"

MCC-GC: "FLIGHT, GC."

MCC-FDO: "FDO, FLIGHT

MCC-FLIGHT: "We need to take the equivalent of a command server TSU (Trajectory Server Upgrade) checkpoint..."'

MCC-FDO: "Yes sir."

MCC-GC: "Copy."

MCC-FLIGHT: "We don't have the old DSC (Dynamic Standby Computer) checkpoint but we have the equivalent capability that we need to do."

MCC-GC: "We'll get that done."

09:18:40 a.m. - MCC-Commentator: "...at an altitude of about 207,000 feet en route to the Kennedy Space Center in Florida and a touchdown that was anticipated to occur about two-and-a-half minutes ago. Flight controllers received no further communications with the spacecraft after about 8 a.m. Central time and no further tracking data from the spacecraft was gained from C-band tracking radar at the Merritt Island tracking station in Florida."

09:18:58 a.m. - MCC-FLIGHT: "GC, FLIGHT."

MCC-GC: "FLIGHT, GC."'

MCC-FLIGHT: "You understand how to do the end-of-file log tapes we need...

MCC-GC: "Yes sir."

MCC-FLIGHT: "...in the checklist? OK."

09:19:14 a.m. - MCC-Commentator: "Contingency procedures in effect in mission control require all operators to conserve all their data and logbooks and notes that have been taken, that being instructed by flight director Leroy Cain for controllers to begin following those steps and secure all information."

09:19:34 a.m. - MCC-FLIGHT: "And folks, listen up again on the flight loop. No phone calls off site outside of this room, our discussions are on these loops, the recorded DVIS (digital voice integrated system) loops only, no data, no phone calls, no transmissions anywhere, into or out."

MCC-GC: "FLIGHT, GC."

MCC-FLIGHT: "GC."

MCC-GC: "We have no way of disabling the black phones."

MCC-FLIGHT: "I understand."

09:20:10 a.m. - MCC-Commentator: "Again, flight director Leroy Cain has declared a contingency. Flight controllers here in mission control are securing all their information, notes and data gathered from the spacecraft. The last communications with Columbia at 8 a.m. Central time as it was descending toward Florida for its landing. At that time, about 207,000 feet above central Texas traveling approximately 12,500 miles per hour, 1,192 miles from its touchdown at Kennedy Space Center. Since 8 a.m., no communications were received with Columbia and no tracking data received through the Merritt Island tracking station, those efforts made. The flight dynamics officer reports no objects tracked through that tracking data."